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why do planets orbit around the sun

Why do the planets rotate around the Sun? First, please note that "rotate" actually is used to describe an celestial body's spin, and "revolve" is used to describe its orbital motion. For example, the Earth completes one rotation about its axis about every 24 hours, but it completes one revolution around the Sun about every 365 days. Anyway, the basic reason why the planets revolve around, or, the Sun, is that the
of the Sun keeps them in their orbits. Just as the Moon orbits the Earth because of the pull of Earth's gravity, the Earth orbits the Sun because of the pull of the Sun's gravity. Why, then, does it travel in an around the Sun, rather than just getting pulled in all the way? This happens because the Earth has a velocity in the direction perpendicular to the force of the Sun's pull. If the Sun weren't there, the Earth would travel in a straight line. But the gravity of the Sun alters its course, causing it to travel around the Sun, in a shape very near to a circle. This is a little hard to visualize, so let me give you an example of how to visualize an object in orbit around the Earth, and it's analogous to what happens with the Earth and the Sun.

Imagine Superman is standing on Mt. Everest holding a football. He throws it as hard as he can, which is incredibly hard because he's Superman. Just like if you threw a football, eventually it will fall back down and hit the ground. But because he threw it so hard, it goes past the horizon before it can fall. And because the Earth is curved, it just keeps on going, constantly "falling," but not hitting the ground because the ground curves away before it can. Eventually the football will come around and smack Superman in the back of the head, which of course won't hurt him at all because he's Superman. That is how orbits work, but objects like spaceships and moons are much farther from the Earth than the football that Superman threw. (We're ignoring air resistance with the football example; actual spacecraft must be well above most of a planet's atmosphere, or air resistance will cause them to spiral downward and eventually crash into the planet's surface. ) This same situation can be applied to the Earth orbiting the Sun - except now Superman is standing on the Sun (which he can do because he's Superman) and he throws the Earth.

The next question, then, is how did Earth get that velocity, since in real life there's no Superman throwing it. For that, you need to go way back to. This page was last updated on January 31, 2016. George Spagna, chair of the physics department at Randolph-Macon College, explains. Stars and planets form in the collapse of huge clouds of interstellar gas and dust. The material in these clouds is in constant motion, and the clouds themselves are in motion, orbiting in the aggregate gravity of the galaxy. As a result of this movement, the cloud will most likely have some slight rotation as seen from a point near its center. This rotation can be described as angular momentum, a conserved measure of its motion that cannot change. Conservation of angular momentum explains why an ice skater spins more rapidly as she pulls her arms in. As her arms come closer to her axis of rotation, her speed increases and her angular momentum remains the same. Similarly, her rotation slows when she extends her arms at the conclusion of the spin. As an interstellar cloud collapses, it fragments into smaller pieces, each collapsing independently and each carrying part of the original angular momentum.

The rotating clouds flatten into protostellar disks, out of which individual stars and their planets form. By a mechanism not fully understood, but believed to be associated with the strong magnetic fields associated with a young star, most of the angular momentum is transferred into the remnant accretion disk. Planets form from material in this disk, through accretion of smaller particles. In our solar system, the giant gas planets (Jupiter, Saturn, Uranus, and Neptune) spin more rapidly on their axes than the inner planets do and possess most of the system's angular momentum. The sun itself rotates slowly, only once a month. The planets all revolve around the sun in the same direction and in virtually the same plane. In addition, they all rotate in the same general direction, with the exceptions of Venus and Uranus. These differences are believed to stem from collisions that occurred late in the planets' formation. (A similar collision is believed to have led to the formation of our moon. )

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